US2363013A - Stable lubricating composition - Google Patents

Description

Patented Nov. 21, 1944 OFFICE STABLE LUBRICATIN G COMPOSITION Arnold J. Mot-way,

Clark Township,

Union County, and John C. Zimmer, Union, N. 3., assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application December 30, 1941, Serial No. 424,926

.- 13 Claims.

The present invention relates to improved stable lubricating compositions, particularly lubricating greases stable against oxidation. More particularly, the invention relates to grease compositions suitable for the lubrication of anti-friction bearings, such as ball bearings and roller bearings.

Grease manufacturers as well as the manufacturers of machine parts realize that greases which are easily oxidized soon lose their lubricating value due to hardening, and the products of oxidation are corrosive to the machine parts. Greases should be stable over a long period of time so that in storage they will not oxidize and break down to liberate corrosive products. It is the practice of anti-friction bearing manufacturers to store their product packed with lubricant. If during storage this lubricant breaks down due to oxidation, corrosive acids are liberated which cause corrosion of the bearing with resultant sticking or locking of the hearing by corrosion products. In operation, the bearing, although of the anti-friction type, does have some friction, and operating at high speeds generates heat which raises the temperature of the hearing appreciably above the temperature of the surrounding atmosphere. Unless precaution is taken, this higher temperature will cause a lubricant to oxidize, depositing a coating of so-called varnish over the surface of the bearing. This varnish is gummy and sticky and gradually hardening and reduces the efficiency of the bearing, or even causes it to lock or freeze, thus rendering it useless. It is customary to put antifriction bearings in operation in a. wide variety of places where a likewise wide variety of temperature conditions prevail. Lubricated-forslife bearings are now being used in a number of inaccessible places, and it is obvious that the life of the bearing and the machine will depend on the life of the lubricant. The'lubricant must therefore be capable of withstanding a wide variation in temperature without oxidation, gum formation, or the loss of lubricating value. Freedom from oxidation is a desirable characteristic not only in greases for life-time bearings, but for greases in general as well. Besides being chemically stable, greases should not separate physically. This phenomenon of physicalseparation is known as bleeding.

Recognizing the desirability of preventing in so far as possible the oxidation of greases and the ensuing detrimental results, it has become the practice to add an oxidation inhibitor to greases. In the usual type of grease prepared from calcium and/or sodium soaps, particularly when such greases have an alkaline reaction, most of these inhibitors are fairly effective and prevent oxidation to a considerable degree. However, greases prepared on the acid side, i. e., having an acid reaction, are not appreciably stabilized against oxidation by the oxidation inhibitors found to be most effective in an alkaline grease.

The most effective and generally accepted test for oxidation is the Norma-Hofimann bomb test described in the paper An Accelerated Oxidation Test for Chemical Stability of Lubricating Greases" by F. L. Wright presented before the 4th Annual Convention of the National Association of Lubricating Grease Manufacturers Inc,

, October 12-13, 1936. By this test, using a glass catalyst, a grease to be considered stable against oxidation should withstand 100 hours at 210 F.

'with no more than a 5 lb. drop in oxygen pressure.

stabilize acid reacting greases against oxidation This and other objects of the invention will be apparent from the following description.

It has now been discovered that the addition of both phenyl alpha-naphthylamine and a zinc soap to an acid reacting grease effectively stabilizes the grease against oxidation. Phenyl' alpha-naphthylamine has been used effectively in basic greases as an anti-oxidant but has been found to be relatively ineffective in an acid grease. The zinc soaps have not heretofore been looked upon as having any anti-oxidant properties rather as oxidation accelerators in catalysts.

Although a wide range of lubricating oils may be employed, in general, the base oil comprises an oil having a viscosity in a range of from about 35 to 1100 seconds at 210 F., a viscosity index of above 20 Deane and Davis, and a good resistance to oxidation. However, in preparing the compositions of this invention, it is preferred to use a base oil having a viscosity of from 40 to 55 seconds S. U. V. at 210 F.

The acids utilized for the production of the metal soaps used in the making of the grease may be either hydrogenated fish oil acids, palmitic, stearic, oleic, naphthenlc acids, or oxidized wax acids, or any other fatty acid or fat commonly used as a soap stock. The metal ion of such as lithium. It is preferred, however, to use a mixture of lithium and aluminum soaps consisting of a'major proportion of lithium soap and a minor proportion of aluminum soap.

Any of the methods generally used in the production or acid greases containing fromv 10 to 35% soap are suitable here. The acid soaps may be made separately and then incorporated in the oil. However, customarily the soap stock .is dissolved in a portion of the lubricating oil by means of gentle heating and stirring. Sumcient metal hydroxide or other water-soluble salt of the metal to neutralize the soap stock is then added and the mixture stirred until the reaction is complete,

after which suiilcient fatty acid is added to give an acid reaction or an amount of metal hydroxide may beuse'd for the neutralization of the soap stock which will incompletely neutralize the soap stock leaving the mixture with a slight acid reacv tions may be secured by varying the soap content of the grease in a particular oil within the limits specified, or by manipulating both the soap content and the viscosity of the lubricating base oil.

The anti-oxidantsused in accordance with this invention consist of a mixture of phenyl a-naphthylamine, phenyl beta naphthylamine or. diphenylamine and a zinc soap such as zinc phenyl stearate. The proportion of combined anti-oxi-' dants ranges from about 0.5% to 2% by weight of the grease. The amount of phenyl a-naphthylamine used will range between 0.1 and 1% and the amount of zinc soap between 0.4 and 1.5%. In the formation of the zinc soaps, any of the acids previously enumerated may be used although it is preferred to use naphthenicacid. Among the many zinc soaps found to be useful for the purposes of this invention, zinc stearateseems'to occupy a unique position in that while it is equally eflicaceous in enhancing the inhibiting power of phenyl a-naphthylamine in acid greases, it is not recommended for general use for the reason that it has a somewhat adverse effect on the grease structure causing the grease to be soft and separate some oil.

The following examples will serve to illustrate specific embodiments of the invention:

Exmrm 1 55 point oil) Hyd fed fish n ms Percent V Phenyl a-naphthylamine 0.2 ro'gena ac 13.00 LiOH (54% lithium hydroxide) 2.05 Mb we Aluminum stearate 0.50 Hours Zinc naphthenate 0.50 '5# drop 18 Lulgricating oil (low. pour Coastal oil) 41.875 15# drop 62' Lu ricating oil (low viscosity, low pour point oil) 41.875 P t Phe la-na hth lamine .2 cm W p y o a Hydrogenated fish oil acids 13.00 65 LloH I 2.05 Aluminum stearate 05' In compounding the above formulafthe acid and approximately one-quarter of the oil are charged into a fire-heated kettle equipped with agitators. The mixture is then heated and stirred to a temperature of about 150 F. 'or until all the acid is melted and dissolved in the oil, and then the lithium hydroxide, dissolved in boiling water, is added to the acid-oil solution. Heating and agitation is continued and the temperature permitted to slowly rise until it reaches about 200 1''. The aluminum stearate is then added and the heating and stirring continued along with intermittent additions of lubricating oil until all but a small portion or the oil has been included. Heating and stirring is'continued until the grease becomes fluid, about 370 F. The phenyl a-naphthylamine and zinc naphthenate dissolved inthe remainder of the oil are then added, heating is then discontinued and the grease stirred until the temperature has dropped to below 100 F. The grease is then drawn. This grease, when tested in the Norma Hofimann oxidation bomb, showed a 5 lb. drop in pressure after 132 hours.

EXAMPLE 2 Per cent Hydrogenated fish oil acids 13.00 L1OH,(54=% lithium hydroxide) 2.05 Aluminum stearate 0.5

Zinc steara 0.5 Phenyl a-naphthylamine 0.5 Lubricating oil (low pour Coastal oil) 41.725 Lubricating oil (low viscosity, low pour point oil) 41.725

' This composition wascompounded as outlined in Example 1.

Norma Hofimann bomb oxidation life Hours 5# drop 300 13#'drop 500 For the purpose oi! ready comparison, the following formulae were compounded according to the method outlined in Example 1 and tested in the Norma Hofimann bomb, giving the following 3 results: I

- Per cent Hydrogenated fish oil acids 13.00 LioH 2.05 40 Aluminum, stearate 0.5

Lubricating oil (low pour Coastal oil) 42.225 Lubricating oil (low viscosity, low pour Lubricating oil (low pour Coastal oil) 42.125

Lubricating oil (low viscosity, low pour Phenyl a-naphthylamine Lubricating oil (low pour Coastal oil) 41.97 Lubricating oil (low viscosity, low pour point oil 41.975

Norma Hofimann bomb oxidation life H 5# drop 75 .l0# drop EXAMPLE 6 Per cent Hydrogenated fish oil acids 13.00 LioH 2.05 Aluminum stearate 0.5 Zinc naphthenate 0.5 Lubricatingoil (low pour Coastal oil) H.975 Lubricating all (low viscosity, low pour point oil 41.975

Norma Hofimann bomb oxidation life Hours l4# drop What is claimed is:

1. An improved stable grease composition comprising a mineral lubricating oil, iii-35% of metal soap, a slight excess of higheriatty acid."

and .5-2% oi an oxidation inhibitor consisting of a mixture oi from .l-l% of an oil-soluble organic amine selected from the group consisting of phenyl alphamaphthylamine, phenyl betanaphthylamine di phenylamine and from .d-l.5% of a zinc soap.

2. An improved stable greasecomposition comprising a mineral lubricating oil, ill-35% of metal scan, a slight excess oi free higher fatty acid, and .5-2% of an oxidation inhibitor consistin of a mixture of from .l-l% or an oil-soluble aromatic amine selected from the group consisting of phenyl alpha-naphthylamine, phenyl betanaphthylamine and di-phenylamine and from .4=l.5% of zinc naphthenate.

3. An improved stable grease composition comprising a mineral lubricating oil, 10-35%'of a mixture of lithium and aluminum soaps, a slight excess of free higher fatty acid, and .5-2% of an oxidation inhibitor consisting of a mixture of .1l% of phenyl a-naphthylamine and .*1.5% or a zinc soap.

4:. An improved stable grease composition comprising a mineral lubricating oil, 10-35% of a mixture of lithium and aluminum soaps, a slight excess of free higher fatty acid, and .5-2% of an oxidation inhibitor consisting of a mixture of .l-1% of phenyl beta naphthylamine and .4-1.5% of a zinc soap.

5. An improved stable grease composition comprising a mineral lubricating 011, 10-35% of a lithium soap, a slight excess of free higher fatty acid, and .5-2% of an oxidation inhibitor consistlng of a. mixture of .1-1% of phenyl a-naphthylamlne and .51.5% of a zinc soap.

7. An improved stable grease composition comprising a mineral lubricating oil, 10-35% of lithium soaps of the hydrogenated fish oil acids, a slight excess of freehigher fatty acid, and .5-2% of an oxidation inhibitor consisting of a mixture of .1-1% of phenyl a-naphthylamine and .4-1.5% of a Zinc soap.

8. An improved stable grease composition comprising a mineral lubricating oil, 10-35% of a metal soap, a. slight excess of hydrogenated fish oil acids, and .5-2% of an oxidation inhibitor consisting of a. mixture of .1-1% of phenyl anaphthylamine and .41.5% of a zinc soap of phenyl stearic acid.

9. An improved'stablegrease-composition eonsisting of a low viscosity, low pour mineral lubrislstlng of a. mixture of .1-1% of phenyl a-naph-- thylamine and .41.5% of a zinc soap.

6. An improved stable grease composition comprising a mineral lubricating oil, 10-35% of lithium soaps of the hydrogenated fish oil acids and aluminum stearate, a slight excess of free acid, and .5-2% of an oxidation inhibitor concating oil, 15.5% of a mixture of lithium and aluminum soaps, a slight excess of free higher fatty acid, and 1% of an oxidation inhibitor consisting of .5% phenyLa-naphthylamine and .5% of a zinc soon;

10. An improved stable grease composition consisting of a low viscosity, low pour mineral lubricating oil, 15% lithium soaps of hydrogenated fish oil acids, 0.5% of aluminum stearate, a slight excess of hydrogenated fish oil acids, and 1% of an oxidation inhibitor consisting of .5% phenyl a-naphthylamine and .5% of a zinc scan.

11. An improved stable grease composition consisting of a low viscosity, low pour mineral lubrieating oil, 15% lithium soaps of hydrogenated fish oil acids, a slight excess of hydrogenated fish oil acids, and 1% of an oxidation inhibitor consisting of .5% phenyl a-naphthylamine and .5% of a zinc oleate.

12. An improved stable grease composition con slsting of a low viscosity, low pour mineral lubricating oil, 15.5% of a mixture of lithium and aluminum soaps, a slight excess of free higher fatty acid, and as an oxidation inhibitor, 0.5% phenyl a-naphthylamine and 0.5% of zinc naphthenate.

13. In a grease composition comprising a mineral lubricating oil, grease producing amounts of metal soap and a slight excess of free higher molecular weight fatty acid, the improvement which consists in incorporating in the grease a small amount, sufficient to inhibit deterioration of the grease, of an oxidation inhibitor consisting of a mixture of from .1-1% of an oilsoluble organic amine selected from the group consisting of phenyl a-naphthylamine, phenyl bnaphthylamine and di-phenylamine, and .4-1.5%

of a. zinc soap.

ARNOLD J. MORWAY. JOHN C. ZIMMER.